Comprehensive Analysis of GRAS Gene Family and Their Expression under GA3, Drought Stress and ABA Treatment in Larix kaempferi

The GRAS family transcription factors play important roles in regulating plant growth and responses to abiotic stress, which can be utilized to breed novel plants with improved abiotic stress resistance. However, the GRAS gene family has been largely unexplored for tree species, particularly for Larix kaempferi, which has high economic and ecological values, challenging practices for breeding abiotic stress-resistant L. kaempferi. In order to improve the stress resistance by regulating the transcription factors in L. kaempferi, we identified 11 GRAS genes in L. kaempferi and preliminarily characterized them through comprehensive analyses of phylogenetic relationships, conserved motifs, promoter cis-elements, and expression patterns, as well as protein interaction network prediction. The phylogenetic analysis showed that the LkGRAS family proteins were classified into four subfamilies, including DELLA, HAM, SCL, and PAT1, among which the SCL subfamily was the largest one. Conserved motif analysis revealed many putative motifs such as LHRI-VHIID-LHRII-PFYRE-SAW at C-terminals of the LkGRAS proteins; we discovered a unique motif of the LkGRAS genes. Promoter cis-acting element analysis exhibited several putative elements associated with abiotic stresses and phytohormones; the abscisic acid-responsive elements (ABRE) and G-box are the most enriched elements in the promoters. Through expression profiles of LkGRAS genes in different tissues and under drought-stress and phytohormones (GA(3) and ABA) treatments, it was demonstrated that LkGRAS genes are most active in the needles, and they rapidly respond to environmental cues such as drought-stress and phytohormone treatments within 24 h. Protein interaction network prediction analysis revealed that LkGRAS proteins interact with various proteins, among which examples are the typical GA, ABA, and drought-stress signaling factors. Taken together, our work identifies the novel LkGRAS gene family in L. kaempferi and provides preliminary information for further in-depth functional characterization studies and practices of breeding stress-resistant L. kaempferi.